Cho et al.
Degenerate Multi-Photon Properties of Spirofluorene Derivatives
were synthesized according to previously reported
methods.
3. RESULTS AND DISCUSSION
Scheme 1 shows a synthetic route of fluorene-based
chromophores (Compound 1, 2, and 3) for comparing
multi-photon properties. Synthesized vinyl compounds
were coupled with 9,9-bis(4-octyloxyphenyl)-2,7-dibromo-
fluorene by Heck reaction. The fluorene unit at the
9-position possesses bulky alkoxyphenyl substituents
which can increase solubility, and restrict aggregation of
molecules. All compounds were adequately characterized
2.1.1. Synthetic Procedure for Compound 1, 2 and 3
9,9-Bis(4-octyloxyphenyl)-2,7-dibromofluorene (12 mmol),
vinyl-substituted compound (30 mmol), palladium acetate
(0.08 mmol), tri-o-tolylphosphine (0.08 mmol), and trib-
utylamine (20 mL) in 100 mL of dimethylforamide
were refluxed for 24 h. After completion of the reac-
tion, the solution was concentrated and poured into
methanol to give a yellowish crude product. The pre-
cipitate was purified by a column chromatography using
n-hexane/methylene chloride (4:1 in vol.) as an eluent.
The pure compound was then obtained by recrystallization
with methanol and methylene chloride.
1
by H NMR, MALDI-TOF MS, UV/vis absorption, and
fluorescence data.
Figure 1 shows the one-photon absorption and fluores-
cence spectra for compound 1, 2, and 3. Their absorp-
tion and emission are clearly red-shifted from 399 nm to
417 nm and from 440 nm to 494 nm with the increase of
the strength of electron donors; N-ethylcarbazole < triph-
enylamine < N,N-dibutylaniline. This red-shift results
from the stabilization of the one-photon-allowed 1Bu state
by the type of amino groups. The fluorescence quan-
tum yields (ꢅf ꢃ for 1, 2, and 3 decrease with increasing
donor strength, which might be originated from nonradia-
tive decay rate (knrad) (Table I). We have also observed
these phenomena in similarly substituted spirofluorene
compounds.9
The 2PA and the 3PA properties were measured by
direct nonlinear transmission method in THF solution with
concentration of 7.8 mM/L at 775 and 1310 nm as the
probing wavelengths for the 2PA and the 3PA, respectively.
AF 350 was used as a reference solution.10 According to
the nonlinear absorption theory, the intensity change of
the incident laser beam along the optical propagation path
z can be described as:5
2.1.1.1. Compound 1. 1H NMR (300 MHz, CDCl3ꢃ:
ꢄ = 8.13 (2H, s), 8.08 (2H, d), 7.81 (2H, d), 7.55–6.93
(24H, m), 6.73 (4H, s), 4.35 (4H, q), 4.11 (4H, t), 1.89
(4H, m), 1.78–1.11 (20H, m), 0.99 (6H, t), 0.89 (6H, t);
MS (EI): m/z 1012.6 (M+1ꢃ+.
2.1.1.2. Compound 2. 1H NMR (300 MHz, CDCl3ꢃ:
ꢄ = 7.68 (2H, d), 7.47 (4H, d), 7.34 (4H, d), 7.29–6.96
(32H, m), 6.76 (4H, d), 3.88 (4H, t), 1.73 (4H, m), 1.46–
1.18 (20H, m), 0.86 (6H, t); MS (EI): m/z 1113.6 (M+1ꢃ+.
2.1.1.3. Compound 3. 1H NMR (300 MHz, CDCl3ꢃ:
ꢄ = 7.67 (2H, d), 7.46 (4H, d), 7.36 (4H, d), 7.21–7.00
Delivered by Ingenta to: McMaster University
(6H, m), 6.87–6.75 (6H, m), 6.62 (4H, d), 3.91 (4H, t),
IP: 5.62.154.195 On: Wed, 15 Jun 2016 15:55:13
3.29 (8H, t), 1.75 (4H, m), 1.59 (8H, m), 1.49–1.21
Copyright: American Scientific Publishers
(28H, m), 0.98 (12H, t), 0.89 (6H, t); MS (EI): m/z 1032.7
(M+1ꢃ+.
2.2. Spectroscopic Measurements
dIꢆzꢃ
UV/Vis absorption and fluorescence spectra were
recorded on a Shimadzu 310pc spectrophotometer and a
Horiba/Jobin-Yvon spectrofluorometer (SPEX 270M) in a
THF solution (1×10−5 M for all compounds). Coumarin
102 (Aldrich, 99%, ꢅf = 0.93 in ethanol) was used as
a reference for the fluorescence quantum yields. 2PA
and 3PA cross-section were measured by direct nonlinear
transmission method (775 nm and 160 fs laser pulses for
2PA and 1310 nm and 160 fs laser pulses for 3PA) in THF
solution.
= −ꢇIꢆzꢃ−ꢈI2ꢆzꢃ−ꢉI2ꢆzꢃ−···
(1)
dz
Here Iꢆzꢃ is the beam intensity through the absorbing
medium, and ꢇ, ꢈ, and ꢉ are the one-, two- and three-
photon absorption coefficients of the absorbing medium.
If the linear absorption is negligible at the excitation fre-
quency (v) and a degenerate 2PA or 3PA are the major
mechanism for the nonlinear absorption, the solutions of
Eq. (1) for the degenerate 2PA process is:
Iꢆ0ꢁvꢃ
Iꢆzꢁvꢃ =
(2)
2.3. Two-Photon Microfabrication
1+ꢈꢆvꢃzIꢆ0ꢁvꢃ
A titanium sapphire laser mode-locked at 80 MHz and a
780 nm wavelength with pulses of less than 100 fs were
utilized as the light source for two-photon based micro-
fabrication. A set of two galvano mirrors was used to
move the focused laser beam in the horizontal plane, and
a piezoelectric stage was used for the vertical alignment
of the beam. 0.1 wt% of compound 2 was mixed with
a photo-curable acrylic resin (SCR-500). The laser beam
was closely focused on the volume of the resin through a
microscope with a high numerical aperture lens.
Pd(OAc)2
R
R
P(o-tolyl)3
Br
Br
Et3N
+
R
DMF
H3C(H2C)7O
O(CH2)7CH3
H3C(H2C)7O
O(CH2)7CH3
N
R:
*
N
*
N
,
,
*
1
2
3
Scheme 1. Synthetic route for compound 1, 2, and 3.
J. Nanosci. Nanotechnol. 10, 6958–6961, 2010
6959
Cho, Namchul
